2018-10-16_PERMIT FILE - M2018039 (2)

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Colorado State University - Extension } Seasonal Water Needs and Opportunities } *Mw for Limited Irrigation for Colorado Crops Fact Sheet No. 4.718 Crop Series I Irrigation by J. Schneekloth and A.Andales' Crop water use,consumptive use and net water requirement to the entire field,in- Quick Facts evapotranspiration(ET),are terms used crease the amount of water or multiply by the interchangeably to describe the water con- efficiency(or inefficiency)of the irrigation • Knowing seasonal crop water sumed by a crop.This water is mainly used system.Looking at the above example,the requirements is crucial for for cooling purposes;a negligible amount is net water requirements,after subtracting ef- planning your crop mixture. retained by the crop for growth.For more fective rain,are 23 inches for sugar beets and information on ET refer to Colorado State 15 inches for corn.If the irrigation system is • Net crop water requirements University Extension Fact Sheet 4.715,Crop 85 percent efficient,apply 27 inches(gross are estimated using models, Water Use and Growth Stages. irrigation amount)to the sugar beets crop based on weather variables. Water requirements for crops depend and 17.6 inches to the corn crop to store the • To irrigate for the greatest mainly on environmental conditions.Plants net water requirement in the crops'root zone. return, producers need use water for cooling purposes and the driv- Now the difference between the seasonal to ing force of this process is prevailing weather gross water requirements of sugar beets and e understand how crops r conditions.Different crops have different wa- corn is 52 percent.The difference in the gross respond to water, how crop ter use requirements,under the same weather irrigation requirement amounts increases as rotation enhances water conditions.Crops will transpire water at the the irrigation system efficiency decreases. availability,and how changes maximum rate when the soil water is at field in agronomic practices affect capacity.When soil moisture decreases,crops Net Crop Water water needs. have to exert greater forces(energy)to extract water from the soil.Usually,the transpiration Requirement rate doesn't decrease significantly until the Net crop water requirement is estimated soil moisture falls below 50 percent of avail- using models that are based on weather vari- able water capacity. ables.Estimate seasonal crop water require- 7 .' Knowing seasonal crop water require- ment by using these models and averaging ments is crucial for planning your crop plant- weather conditions over many years.This will ing mixture,especially during drought years. create an average weather year.Tables 1 and For example,in the Greeley area,the seasonal 2 are a summary of net water requirements - water use of sugar beets is 30 inches,while of different crops and effective precipitation corn uses only 22 inches of water.That means for different locations in eastern Colorado to fully irrigate sugar beets you need to apply and western Colorado,respectively.To figure 36 percent more water as compared to corn. the net irrigation requirement,subtract the These water requirements are net crop water effective rain(Average Effective Precipita- use,the amount that the crop will use(not tion from Tables 1 and 2)from the net crop counting water losses)in an average year, water requirement.The gross irrigation water given soil moisture levels don't fall below requirement is the net irrigation requirement critical levels.Under ideal conditions,this net divided by the irrigation system efficiency water requirement is reduced by the effective (fraction of one).For example,corn for grain rain,which for the Greeley area is 7 inches for in Burlington requires 26 inches of water. the growing season. Effective precipitation is 11.28 inches for the The rest of the crop water requirement season;therefore the net irrigation require- must be supplied by irrigation.No irrigation ment is 14.72 inches.The gross irrigation system is 100 percent efficient,so to apply the requirement for a center pivot with 80 per- ©Colorado State University cent irrigation efficiency is 18.4 inches.For Extension.4/03. Revised 9/09. V.Schneekloth,Colorado State University Extension a furrow irrigation system with 55 percent www.ext.colostate.edu water resource specialist,U.S.Central Great Plains irrigation efficiency,the gross irrigation 5] p Research Station,Akron,Colorado;A.Andales,Colorado requirement is 26.7 inches. O State University assistant professor,soil and crop sciences.912009